This project has been designed to test the hypothesis that there exists employees in the workplace who are genetically predisposed to the myelotoxic effects of polycyclic aromatic hydrocarbone. Testing will be accomplished by examining the effects of benzo(a)pyrene, (BP), an ubiquitous pollutant, in two genetically defined mice strains, the C57BL/6 (B6) and DBA/2 (D2). The carcinogen will be administered intragastrically, and its immunosuppressive effects evaluated by a determination of the Natural Killer (NK) and bone marrow NK stem and stromal cell activities at 4, 8, and 12 weeks of age. Since NK activity has been shown to be predetermined by the genetic make-up and speculated as the first line of defense in the immunosurveillance against cancer, the results gathered in this study are expected to provide information regarding possible genetic predisposition to myelotoxic effects of chemicals in the working environment. Evaluation of the bone marrow NK stromal and stem cell activities will be accomplished by fibroblast colony formation (Marrow stromal Cell Assay) and the ability for bone marrow reconstitution of NK activity in X-irradiated syngeneic mice. The results from these particular studies will aid in the mechanistic interpretation for the cellular changed observed in the genetically defined animals. While the pathogenesis for human cancer has yet to be completely understood, increasing information is now becoming available to suggest that there are employees who may be genetically predisposed to the myelotoxic effects of polyaromatic hydrocarbons. The results derived from this proposed project will be expected to aid in our understanding of what influencing such predisposition may have upon the possible workshop related carcinogenesis.